Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School



The following study arose from the discussion of a problem in a course in theoretical physics at South Dakota State College during the Winter quarter 1956-1957. The problem is stated as follows: “A symmetrically magnetized cylindrical magnet is rotating with constant angular velocity about its axis of symmetry. A straight wire at right angles to and in the plane of the axis of the magnet is arranged so that it can be rotated about the same axis. Is there an e.m.f. along the wire (a) when it is at rest, (b) when it is rotating with the magnet? Explain why.” In attempting to answer this question, one becomes involved in the question of whether or not the lines of magnetic induction rotate with the magnet since in elementary electromagnetic theory the e.m.f. induced depends upon the rate at which the lines cut through the wire. Historically this rotation or non-rotation of the lines was at one time the primary point of interest in the so called “unipolar” induction experiments. The literature reveals an impressive list of experimenters who have investigated unipolar induction and have attempted to interpret their results in terms of an acceptable “cutting line” theory. This work culminated in a comprehensive paper by Tate in which he summarizes the experimental work and follows Swann in explaining the observed results and in proposing an acceptable “moving line” theory. The unfamiliar nature of some of their conclusions and the lack of experimental verification for others justifies the following study of the electric field of moving magnets. The theory of Swann is developed and his “moving line” theory is stated. Experimental verification of this theory is investigated and questioned. Then an experiment designed to test this theory is described and its results are discussed.

Library of Congress Subject Headings

Electromagnetic theory


Includes bibliographical references



Number of Pages



South Dakota State University